it's a good conversion IMO. give it a go. Matt black had a conversion available.
I have been following your project with interest, and from what I remember you had to do similar modification as a result of the VAG sump i think it was? When are you hoping to get it back on the road?
I can't afford to start the project till at least September at the earliest, think it will be more December time tbh! Will have started by graduate job by then which hopefully!
When/If it happens I am thinking:
Buy a cheap 172, aim for a ph2 but maybe a ph1. Obviously it doesn't need to have much history if any as engine will be coming out, would like it to be tidy looking but that's not a must (scruffy would make it more of a sleeper i guess!) Brakes and suspension condition wouldn't be to important as would be upgraded anyway.
Then I would be tempted to try and get a complete meg, hopefully written off with rear end damage. That would be ideal, then gut it for what I need/want and sell the rest as parts, maybe make a little money back. This might not be ideal though, need to look at prices first really.